Accurate control mechanisms that direct the eyes and head toward objects in our environment are fundamental to proper visual function and successful interactions with the our environment. For primates, with their frontal eye placement and highly developed retinas, vision may be the preeminent sensory modality employed in orienting and interacting with the surrounding environment. The relationship between the motor and visual systems is indicated by the patients who present in the clinic with complaints of visual dysfunction when, in fact, they suffer from a pathological oculomotor system. While much progress has been made in gaining an understanding of the orienting mechanisms that rotate the eye in the orbit, less is known of the neuronal mechanisms regulating the head movements that naturally move the eyeball in space. The proposed investigation of the cerebellar vermal lobules VI & VII (vermis-6,7), fastigial nucleus (FN), and nucleus reticularis tegmenti pontis (NRTP) should help obviate this limitation and increase our knowledge of sensori-motor signal processing that is fundamental to regulating visually-guided movements. The specific goal of the proposed study is to clarify the role that these neural structures play in the control of visually guided motor behavior as exemplified by coordinated eye and head movements. Attention will be focused on determining the mechanisms that vermis-6,7 and FN employ in ensuring the accuracy of gaze saccades and gaze pursuit. Also of keen interest will be the inhibitory mechanisms operating in NRTP. The proposed investigations of sensori-motor mechanisms in vermis-6,7 and FN will contribute to the long-term goal of providing a comprehensive picture of cerebro-ponto-cerebellar roles in regulating visually guided motor behavior. Ultimately, the knowledge gained from these experiments should provide a better understanding of anatomic functional specificity that will aid the physician in identifying and treating neurological diseases. The collaboration between the principal investigator and a neuro-ophthalmologist, will ensure the rapid implementation of significant findings in the development of clinical tests.